Surveillance methods lead to maternal mortality variations, possible misclassifications

Key takeaways:

• U.S. maternal mortality rates varied based on the type of surveillance method used.
• From 1999 to 2002 and 2018 to 2021, maternal mortality increased for white women and decreased for Black and Hispanic women.

Differences in U.S. cause of death surveillance methods may cause variations in currently high reported maternal mortality rates, researchers reported in the American Journal of Obstetrics & Gynecology.

“National Vital Statistics System (NVSS) reports show that maternal mortality rates in the United States have continued to increase from 17.4 in 2018, to 20.1 in 2019, 23.8 in 2020 and 32.9 per 100,000 live births in 2021. Do these relatively high and rising rates of maternal death indicate changes in obstetrical factors, maternal medical conditions or maternal mortality surveillance?” K.S. Joseph, MD, PhD, professor in the department of obstetrics and gynecology at the University of British Columbia School of Population and Public Health and investigator at British Columbia Children’s Hospital, and colleagues wrote. “Addressing this question requires clarity with regard to definitions, especially the distinction between maternal death and pregnancy-associated death.”

Joseph and colleagues identified all U.S. maternal deaths from 1999 to 2021. Deaths were identified using NVSS methodology in which deaths in pregnancy or postpartum were indicated by a positive pregnancy checkbox on the death certificate or by an alternative formulation in which deaths had pregnancy listed as a possible cause of death on the death certificate. Researchers measured frequencies of major cause of death categories in deaths of females aged 15 to 44 years, maternal deaths, direct obstetrical deaths defined as deaths from obstetrical causes and indirect obstetrical deaths defined as deaths from maternal medical conditions aggravated by pregnancy or pregnancy management. Researchers compared maternal mortality rates per 100,000 live births in 1999-2002 and in 2018-2021. Maternal mortality data for the 2003 to 2017 time period was not used as all deaths during that time were replaced with pregnancy chapter codes if the pregnancy checkbox was checked on the death certificate.

Maternal mortality per 100,000 live births identified by NVSS increased by 144% from 9.65 in 1999-2002 to 23.6 in 2018-2021. Maternal mortality increases were observed among all racial and ethnic groups. Direct obstetrical deaths per 100,000 live births increased from 8.41 in 1999-2002 to 14.1 in 2018-2021, and indirect obstetrical deaths per 100,000 live births increased from 1.24 in 1999-2002 to 9.41 in 2018-2021, the researchers reported.

Overall, 38% of direct and 87% of indirect obstetrical deaths in 2018-2021 were identified by a positive pregnancy checkbox on the death certificate.

Using the alternative formulation where maternal deaths had pregnancy listed as a possible cause of death on the death certificate, maternal mortality per 100,000 live births increased from 10.2 in 1999-2002 to 10.4 in 2018-2021. In addition, direct obstetrical deaths per 100,000 live births decreased from 7.05 in 1999-2002 to 5.82 in 2018-2021 using the alternative formulation vs. NVSS, according to the study.

From the 1999-2002 to the 2018-2021 period, deaths caused by the following decreased:

• preeclampsia (0.93 to 0.48 per 100,000 live births);
• eclampsia (0.55 to 0.3 per 100,000 live births );
• postpartum hemorrhage (0.35 to 0.32 per 100,000 live births);
• puerperal sepsis (0.11 to 0.07 per 100,000 live births);
• venous complications (0.24 to 0.17 per 100,000 live births);
• amniotic fluid embolism (0.94 to 0.68 per 100,000 live births); and
• blood clot embolism (0.45 to 0.26 per 100,000 live births).

During the same period, deaths caused by the following increased:

• deaths from adherent placenta (0 to 0.15 per 100,000 live births);
• renal and unspecified causes (0.46 to 1.72 per 100,000 live births);
• cardiomyopathy (0.63 to 0.74 per 100,000 live births); and
• preexisting hypertension (0.14 vs. 0.47 per 100,000 live births).

Non-Hispanic white women had an increase in maternal mortality per 100,000 live births from 6.66 in the 1999-2002 to 8.22 in the 2018-2021 period while maternal mortality per 100,000 live births decreased among Black (25.7 to 23.8) and Hispanic (9.43 to 7.46) women. Compared with other races/ethnicities, Black women had disproportionally higher rates of specific causes of maternal mortality, such as cardiomyopathy.

“Identifying maternal deaths by requiring the mention of pregnancy among the multiple causes of death provides a more accurate, clinically coherent and compelling perspective on maternal mortality in the United States and can serve as the evidentiary basis for clinical and public health initiatives,” the researchers wrote.